crystal

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A homogenous solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between constituent parts.
• noun The unit cell of such a pattern.
• noun A mineral, especially a transparent form of quartz, having a crystalline structure, often characterized by external planar faces.
• noun A natural or synthetic crystalline material having piezoelectric or semiconducting properties.
• noun An electronic device containing such a material, as one that provides access to a radio frequency.
• noun A high-quality, clear, colorless glass.
• noun An object, especially a vessel or ornament, made of such glass.
• noun Such objects considered as a group.
• noun A clear glass or plastic protective cover for the face of a watch or clock.
• noun Slang A stimulant drug, usually methamphetamine, in its powdered form.
• adjective Clear or transparent: synonym: clear.

from The Century Dictionary.

• noun An English trade-name for a fine quality of white sugar.
• noun In chem. and mineralogy, a body which, by the operation of molecular attraction, has assumed a definite internal structure with the form of a regular solid inclosed by a certain number of plane surfaces arranged according to the laws of symmetry.
• noun Glass. Glass of a high degree of transparency and freedom from color. It is heavier than ordinary glass, because containing much oxid of lead.
• noun Fine glass used for table-vessels or other table-service, or for ornamental pieces. The term is sometimes used as synonymous with cut glass.
• noun The glass cover of a watch-case.
• noun A substance resembling rock-crystal or glass in its properties, especially in transparency and clearness.
• noun In heraldry, the color white: said of that color when described in blazoning a nobleman's escutcheon, according to the system of blazoning by precious stones; pearl, however, is more commonly used.
• noun A very fine wide white durant, once used for making nuns' veils.
• noun In optics. See refraction.
• Consisting of crystal, or like crystal; clear; transparent; pellucid.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Consisting of, or like, crystal; clear; transparent; lucid; pellucid; crystalline.
• noun (Chem. & Min.) The regular form which a substance tends to assume in solidifying, through the inherent power of cohesive attraction. It is bounded by plane surfaces, symmetrically arranged, and each species of crystal has fixed axial ratios. See crystallization.
• noun The material of quartz, in crystallization transparent or nearly so, and either colorless or slightly tinged with gray, or the like; -- called also rock crystal. Ornamental vessels are made of it. Cf. Smoky quartz, Pebble; also Brazilian pebble, under Brazilian.
• noun A species of glass, more perfect in its composition and manufacture than common glass, and often cut into ornamental forms. See Flint glass.
• noun The glass over the dial of a watch case.
• noun Anything resembling crystal, as clear water, etc.
• noun See under Blood.
• noun See under Compound.
• noun a transparent variety of calcite, or crystallized calcium carbonate, brought from Iceland, and used in certain optical instruments, as the polariscope.
• noun any transparent crystal of quartz, particularly of limpid or colorless quartz.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable A solid composed of an array of atoms or molecules possessing long-range order and arranged in a pattern which is periodic in three dimensions.
• noun countable A piece of glimmering, shining mineral resembling ice or glass.
• noun uncountable A fine type of glassware, or the material used to make it.
• noun uncountable, slang crystal meth: methamphetamine hydrochloride.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a protective cover that protects the face of a watch
• noun glassware made of quartz
• noun a rock formed by the solidification of a substance; has regularly repeating internal structure; external plane faces
• noun colorless glass made of almost pure silica
• noun a solid formed by the solidification of a chemical and having a highly regular atomic structure
• noun a crystalline element used as a component in various electronic devices